"Ajimu - Kaigan Monogatari" is a supernatural mystery anime that revolves around the coastal town of Ajimu, a place steeped in folklore and eerie legends. The narrative centers on a group of high school students who become entangled in a series of strange occurrences linked to the town's history. The protagonist, a transfer student named Haruto, arrives in Ajimu and quickly notices the town's peculiar atmosphere. He befriends a local girl named Saki, who is deeply connected to the town's myths, and together they begin to uncover the secrets of Ajimu.

The story unfolds as Haruto and Saki investigate the mysterious disappearances of townspeople and the recurring appearance of ghostly figures near the coastline. They learn that these phenomena are tied to an ancient legend about a cursed ship that sank off the coast centuries ago. The ship's restless spirits are said to haunt the town, seeking to reclaim something lost. As the duo delves deeper, they discover that the curse is tied to a ritual performed by the town's ancestors to appease the spirits, but the ritual was never completed, leaving the town vulnerable to the supernatural forces.

Supporting characters include Haruto's classmates, each of whom has a personal connection to the town's history. Among them is Ryo, a skeptical but resourceful friend who assists in the investigations, and Yuna, a quiet girl who harbors a tragic secret tied to the curse. The group uncovers fragments of the ritual and attempts to piece together the steps needed to break the curse, all while evading the malevolent spirits that grow increasingly aggressive.

The plot intensifies as the characters face moral dilemmas and confront their own fears, with the line between the living and the dead blurring as the curse tightens its grip on Ajimu. The climax involves a race against time to complete the ritual before the spirits claim more victims, culminating in a dramatic confrontation that tests the bonds of friendship and the characters' resolve. The series concludes with a resolution that ties together the threads of the curse, the town's history, and the characters' personal journeys, leaving a lingering sense of closure while hinting at the enduring mysteries of Ajimu.